Zuckerberg will testify April 11 - and, incidentally, will face questioning from lawmakers who in the past received substantial campaign contributions from Facebook sources.

The executives further explained, however, that these ads will be "clearly labeled" as "Political Ad" with "paid for by" information.

"We approached this research as we would any other scientific, medical, or clinical research - ensuring that the research protocol would be consistent with HIPAA regulations, the HHS Office of Human Research Protections regulations, and relevant Institutional Review Board decisions", Valentine said in an emailed statement. "It's clear that data of Europeans have been exposed to a huge risk and I am not sure if Facebook took all the necessary steps to implement change", Jourova said on Friday.

Facebook says page administrators and advertisers will be asked to provide a government-issued ID for verification.

Starting Monday, all 2.2 billion Facebook users will receive a notice on their feeds, titled "Protecting Your Information", with a link to see what apps they use and what information they have shared with those apps. Users won't be able to do anything about it, but at least now they know that Facebook has monitored their mouse movements, nearby devices, messenger histories, and proximity to cell towers all along.

This marks an expansion of Facebook's previous plans on this front, when these measures would have applied only to political ads - typically defined as mentioning a specific candidate - but not to ads that only talk about hot-button issues without mentioning candidates. "This will make it much harder for people to run pages using fake accounts, or to grow virally and spread misinformation or divisive content that way", he said.

Now, anybody that wants to show what are being referred to as "issue ads" will also need to be authorized first. Any advertiser who doesn't pass will be prohibited from running political or issue ads. Neither can they opt entirely out of Facebook's data collection. In all, Facebook says as many as 87 million people might have had their data accessed. Facebook executives took almost five days to respond to the Cambridge Analytica reports. The development immediately follows backlash against the company that it deleted messages its CEOMark Zuckerberg sent in the past to people with whom he was communicating on Messenger.